Noted Forensic Geologist Unravels the Disaster
Just before midnight on March 12, 1928, while Los Angeles slept, the St. Francis Dam gave way, breaking apart and generating a tremendous initial wave over 130 foot high, bringing death and disaster to the people and property in its path. That night w as to become the worst disaster in the history of Los Angeles, with at least 450 people dead, washed away by the waters with no warning of the coming flood.
The tragedy of that night has continued to foster interest on the human tragedy, speculation on what caused the dam to break, and, ultimately, where to lay the blame. Over 70 years later, it is still a controversial topic.
In conjunction with the Library's exhibition, "Remembering the St. Francis Dam Disaster of 1928," the Friends of the Oviatt Library sponsored a talk by Dr. J. David Rogers, a noted authority on the study of what really caused the dam failure.
Introduction by Catherine Mulholland
Nearly 150 people attended the presentation on March 23rd in the University Club. Catherine Mulholland, granddaughter of William Mulholland, the chief engineer for the dam, gave an introduction. Although she was only 5 years old at the time, she remember ed being taken to the site after the flood, and being deeply affected by the view. Her mother's best friend, the wife of the damkeeper, was killed in the flood waters, and is buried at Oakwood Memorial Park in Chatsworth. Most vivid is the memory of her devastated grandfather, who accepted all the blame for the dam's failure, and never recovered from the heavy burden of guilt he was to carry until his death seven years later.
Ms. Mulholland introduced the main speaker, Dr. J. David Rogers, geologist, civil engineer, and leading authority on St. Francis. In a fascinating talk filled with technical details made understandable by Rogers' lay explanations and easy manner, the aud ience was taken back to the beginnings of the dam, in 1922.
Included in the series of dams they decided upon was the St. Francis. Rogers reported that it was built of concrete, because there was not enough earthen material at the sight. The literature on concrete monolith dams had just been published at the time , and St. Francis followed the current technology of the time. The dam was 185 feet high, but during construction the height was increased by another 20 feet, to hold even more water for the burgeoning Los Angeles population. Raising the height without increasing the base was to prove a fatal flaw.
Rogers, a forensic geologist, had a long history of interest in the St. Francis Dam. He wanted to solve the mystery of the failure, and spent many years studying the plans for the dam, visiting the site, examining the rubble left behind, the records of t he dam on the day it broke, and the accounts of survivors. He also studied computer generated stress tests and models, aerial photos taken the following day, and tested pieces of the concrete left behind. Rogers came to the conclusion that the dam failu re was caused by a number of factors, but most significantly by a landslide that night that no one could have foreseen.
That night, a massive landslide of 1 million cubic yards occurred, undermining the east abutment of the dam. It was noted that the road above the dam had dropped one foot that night, and the higher road had dropped 6 feet. It was truly a huge landslide.
As the lower east side gave way with the landslide, at the rate of 1.7 million cubic feet per second, it undercut the dam. The arch of the dam was not able to hold the tension, and the huge dam actually tilted to the east. The west section of the dam th en fell toward the east, while the center remained standing. The released torrent flowed 52 miles to the ocean, taking 5 1/2 hours to get there.
Rogers noted that other factors that played a role in bringing the dam down once the landslide occurred were the poor grade of concrete, which quickly saturated, the lack of knowledge of hydraulic uplift theory at the time, the increase of the height of t he dam, without also increasing the bottom width, and the lack of relief wells. However, he pointed out that most of this knowledge was to come in the near future, and was not available to Mulholland and his designers in 1922. Nor could they have forese en the landslide.
Rogers concluded his talk with the consequences of the disaster-the end of Mulholland's illustrious career, and the creation of the Division of Dam Safety.
